1. Field of the Invention
The present invention relates to a bias circuit for supplying an amplifier of a microwave band, semimillimeter wave band or millimeter wave band, with a bias voltage. More particularly, the present invention is concerned with a bias circuit for supplying the aforesaid amplifier, to which a detector circuit is connected, with a bias voltage.
2. Description of the Related Art
Usually, an amplifier of a microwave band is provided with a diode detector portion at its output side for automatic level control maintaining a level of an output signal at a constant value.
Conventionally, a signal to be input to the diode detector portion is separated from the output signal of the amplifier using a directional coupler. Thus, the directional coupler is required to be provided at output side of the amplifier. A bias circuit is also required to be provided at the output side of the amplifier for supplying the amplifier with a bias voltage.
Therefore, the size of the circuit in the output side of the amplifier is inevitably large. Furthermore, since a part of the output signal is separated in the directional coupler, a level of the output signal is lowered accordingly.